In order to achieve higher surface recording density while maintaining thermal stability, a magnetic recording layer is necessary that has a high perpendicular magnetic anisotropy energy Ku. L10-ordered FePt alloy is a material having higher perpendicular magnetic recording anisotropy energy Ku than the currently employed CoCrPt-based alloys, and has thus has attracted attention as a material for next-generation magnetic recording layers. An example is described in Laid-open Japanese Patent Application Number 2008-91024.
In order to employ such L10-ordered FePt alloy as a magnetic recording layer, it is necessary to reduce the exchange interaction between crystal lattices. In recent years, as disclosed in for example Patent Reference 1 there have been reports of attempts to achieve granularization by addition of non-magnetic material such as SiO2 or C to the L10-ordered FePt alloy. In this context, granularization means that the magnetic crystal grains are magnetically divided by producing a structure wherein magnetic crystal grains made of FePt are separated from one another by crystal grain boundaries of non-magnetic material that surround the magnetic grains.
In order to employ FePt alloy having L10 type crystal structure in a magnetic recording layer, it is necessary to perform (001) crystal orientation of the FePt layer. In this regard, it is widely known that (001) crystal orientation can be performed by employing a suitable material as the under-layer formed below the FePt layer. Laid-open Japanese Patent Application Number 2012-48784 discloses an FePt layer having (001) crystal orientation, due to the use of a MgO under-layer. Also, in order to perform (001) crystal orientation by ordering of the FePt, it is necessary to heat the structure to at least 300° C.
In order to employ an FePt alloy having an L10 type crystal structure in a magnetic recording layer, it is necessary to form a MgO under-layer and to perform (001) crystal orientation by heating the FePt layer thereon. Consequently, if roughness is thereby produced in the under-layer surface, this roughness is enhanced in the FePt layer surface with the result that considerable roughness is produced. If such surface roughness is large, the flyability characteristics are degraded, with the result that good flyability characteristics can be maintained over a long period. In FePt alloy media having an L10 type crystal structures such as have been employed up to the present, corrosion resistance has been a problem, chiefly for the reasons described above, and this needs to be solved.